Electric insulating material



Patented Feb. 7, 1933 UNITED STATES PATENT OFFICE MAX HAGEDORN, OF DESSAU IN .ANHAL'I, OTTO BEICHERT, 0F D'ESSAU-ZIEBIGK IN .ANHALT, AND EUGEN GUHRING, OF DESSAU IN ANHALT, GERMANY, ASSIGNORS TO I. G. FARBENINDUSTRIE AKTIENGESELLSCHAFT, OF FRANKFURT-ON-THE-MAIN,

GERMANY ELECTRIC INSULATING MATERIAL No Drawing. Application filed January 31, 1930, Serial No. 425,056, and in Germany February 13, 1929.

Our present invention relates to new insulating materials for electric purposes, and more particularly to such materials as are composed of a cellulose derivative.

\Ve have found that mixed cellulose esters of lower fatty acidsare particularly suited for use in the manufacture of electric insulating materials without the addition of considerable quantities of heterogeneous substances. lVe may use for the said purpose a mixed ester of cellulose which contains simultaneously in any combination radicals of diiier-ent lower fatty acids, that is to say, of the acids containing up to 5 carbon atoms:acetic acid, propionic acid, butyric I acid, valeric acid. We prefer to use such a mixed ester which contains the radicals of two lower fatty acids, however, those esters derived from more than two acids are meant to be included within our invention. The said cellulose esters may be employed as primary esters or they may be subjected to a hydrolyzing process.

Of the great number of mixed esters of lower fatty acids, we prefer to use a cellulose derivative which contains the acetic acid radical in addition to another lower fatty acid radical. Such a mixed ester has both the good mechanical properties of the cellulose acetate and a high stability towards saponifying agents. Cellulose acetate butyrate has proved to be especially suitable. Thus, for instance, a foil of 0.13 mm. thickness of a cellulose acetate-butyrate containing in the molecule 1% molecular proportions of the acetate acid radical and 1% molecular proportions of the butyric acidradmal calculated on C H O has a sparking potential or dielectric strength of about 16000 volts and of 9500 volts after having been immersed in distilled water for 200 hours.

The superiority of our new insulating materials over those prepared from cellulose acetate can be clearly seen from the following table.

Commercial Cellulose celluloseaoctatebuty acetate rate Thickness Sparking potential of the air-dry product.

Sparking potential after having been immersed for 48 hours in water at 90 p. 11, 4 kilovolts.

8, 2 kilovolts.

6, 8 kilovolts 2, 2 kilovolts Sparking potential of the product in transformer oil.

Sparking potential after having been immersed for 2% hours in oil at 7, 65 kilovolts.

9, 6 kilovoltsv The mixed cellulose esters can be worked up n such a manner that paper or fabrics are lmpregnated with their solutions and are used for taping cables. The materials thus prepared, may, however, also be used for other insulating purposes. There can likewise be used for insulating purposes layers of the mixed cellulose esters alone by covering the cables, surfaces or the like to be insulated with a lacquer of these cellulose derlvatives. We may incorporate into the new insulat- 1ng substance any of the additions which are known in the industry dealing with the manufacture of electric insulating materials such as, for instance, filling materials, pigments, dyes, natural or artificial resins, plastifying or softening agents or another cellulose derlvative.

F onthe manufacture of our new insulating materials, we may use the solvents known in the art; it is advisable, however, to avoid the use of chlorinated hydrocarbons, which split off hydrochloric acid in the course of time. When forming the insulating body with the application of heat and pressure the use of a solvent may be dispensed with.

The following examples serve to illustrate our invention Emaxmple 1.A solution of cellulose acetate-butyrate (1 /2 mol. of acetic acid and 1 mol. of butyric acid) in acetone is cast in the known manner so as to form a film of a strength of 80 to 100 ,a and the fihn cut into tape of a breadth of 25 mm. The electric cables are wound with this tape in a taping machine.

Example 2.- A solution of cellulose-monoacetate-dipropionate in a mixture of alcohol, benzene and acetone in a proportion of 1: 1:7 is cast to foils of a strength of 10 to 20 The foils are used in the known manner together with metallic foils for preparing high tension condensers.

Numerous other embodiments are possible and we contemplate as included within our invention all such modifications and equivalents as fall within the scope of the appended claims.

What we claim is 1. An electric insulator comprising a compound selected from the group consisting of a cellulose acetate-butyrate and a cellulose acetate propionate.

2. An electric insulator comprising cellulose acetate butyrate.

3. An electric insulator comprising cellulose mono acetate dipropionate.

In testimony whereof, we aflix our signatures. MAX HAGEDORN.

OTTO REICHERT. EUGEN GUHRING. 

